1. Field of the Invention
The present invention relates to porous optical fiber base materials, optical fiber base materials and methods for producing them. In particular, the present invention relates to a porous optical fiber base material with improved weight of fine glass powder deposited on a member contained in the material, or improved fine glass powder deposit efficiency, and a porous optical fiber base material capable of affording a reduced number of air bubbles in a sintered body which is obtained by vitrifying deposited fine glass powder by fusion, and the present invention further relates to optical fiber base materials that can be obtained from the aforementioned porous base materials, and methods for producing them.
2. Description of the Related Art
A porous optical fiber base material has conventionally been produced by, for example, as in the outside chemical vapor deposition, depositing fine glass powder on a circumferential surface of axially rotating member of porous optical fiber base material.
In order to deposit the fine glass powder on the circumferential surface of the member, for example, the member is placed in an apparatus, called chamber, which covers the both ends of the member along its axial direction, and fine glass powder is produced around the member with flame formed from fuel gas and material gas thrown from a flame burner provided at a front part of the chamber so that the fine glass powder should be deposited on the member. The chamber is also provided with a mechanism for exhausting unreacted gases, gases generated from reactions, fine glass powder not deposited and the like from an exhaust port provided on the side opposite to the flame burner in the chamber.
A porous optical fiber base material produced by depositing fine glass powder on a member as described above has excellent purity and other-various excellent qualities. That is, in the field of the porous optical fiber base material production, marked progress has been achieved as for quality in recent years.